For over 30 years, buried cables for filled telephone cables were required to meet ASTM B736 which specifies a 0.15 mm (0.006-in.) electrolytic chromium coated steel (ECCS) shield for protection. ECCS is a single reduced tin mill black plate electrolytically coated steel with chromium and chromium oxide. This steel grade has been specified in the fiber optic cable industry for over 25 years. This steel specification was specified for corrosion resistance, protection against rodents, lightning resistance, and use in the field.
At the time the ASTM B736 specification was developed, steel was easily acquired and produced in the U.S. It could also be imported from Japan and a few other countries, and offered at relatively low cost. Unfortunately, there is no longer a U.S. producer and it is getting more difficult to find companies willing to supply this steel. Because of the supply position and the rapid industrialization in China, the cost of steel doubled from 2004 to 2005.
From a flexible packaging perspective the steel used for armored cable is a heavy-gauge product at 0.15 mm (0.006-in.) steel, but this is not the case in the steel industry in general. The 0.15 mm (0.006-in.) gauge is very light for steel mill production and is the preferred minimum gauge level for steel mills that make this product. Although such mills can produce lighter steel, this is very difficult and more expensive.
A study entitled “Corrosion Evaluation of Underground Cable Shielding Materials” conducted by NTIS evaluated various metal and film combinations. These materials were buried in 3 test soil conditions at 1-7 year time frames. Bare aluminum of the 1100 alloy type proved to corrode under some of these conditions. However, the aluminum foil with Ethylene Acrylic Acid (EAA) coated on both sides showed excellent corrosion resistance.